1. Field of the Invention
The present invention relates to an electrostatic charging device for charging a photosensitive drum of an electrophotographic apparatus by utilizing corona discharge, and more particularly to a structure which enables removal and replacement of a corona discharging electrode.
2. Description of the Related Art
As a photosensitive body for use in an electrophotographic apparatus, an organic photo conductor (OPC) is employed increasingly every year for its advantages in terms of cost, safety and wavelength selectivity. Most of the electrophotographic apparatuses marketed as new products in recent years use an OPC of negative charge type. An electrostatic charging device has been known as an apparatus for providing a negative charge to the OPC. The charging device can be grouped into a contact type and a non-contact type depending on whether the device is in contact with the OPC or not, and each type has advantages and disadvantages, so that appropriate type is selected for use, accordingly. The charging device of non-contact type utilizes mainly corona discharging and, therefore, such device is called a corona discharging device. Scorotron-type corona discharging device is used predominantly for its advantage in charge stability. In the charging device of scorotron-type, OPC charging is controlled by application of voltage with a magnitude of thousands of volts to the control grid.
Deterioration or fouling of discharging electrode of the corona discharging device causes irregular corona discharging and hence uneven charge potential on the OPC surface, with the result that troubles with image formation that is the basic function of the electrophotographic apparatus will be invited. The discharging electrode of the corona discharging device is subjected to application of high voltage, and therefore, the electrode has a serviceable life which is shorter than that of the electrophotographic apparatuses itself, so that generally the corona discharging device is replaced as a whole or as a process unit. As the discharging electrode of the non-contact type corona discharging device, two types of electrode are available including wire type and edge type (also referred to as sharp pin type) are available, both of which are used extensively. Especially, an edged electrode plate used for charging by the corona discharging device is made of thin metal sheet and formed with an array of sharp edges disposed in a sawtooth-like arrangement.
When changing the edged electrode plate because of deterioration of the electrode edges or for any other reason, it has been a conventional practice to remove the entire corona discharging device (i.e. charging device) from the process unit of the electrophotographic apparatus and then change the faulty edged electrode plate by disassembling the charging device, thus the procedure for the replacement of the edged electrode plate having being quite troublesome. Specifically, many of the charging devices such as corona discharging device operable by utilizing corona discharging are of scorotron type which uses both edged electrode plate and the control grid for controlling the charge, so that it is necessary to remove the control grid in changing the edged electrode plate. The control grid is provided with a thin mesh plate which is difficult to handle, and there is a fear that the control grid may be deformed during changing of the edged electrode plate.
The present invention has been made in light of the above-described problems and, therefore, it is an object of the invention to provide an electrostatic charging device, which is capable of allowing the edge electrode plate to be inserted into and removed from the charging device easily merely by slidably moving only the edged electrode plate.
In order to achieve the object, there is provided a electrostatic charging device for charging a photosensitive drum, which comprises an edged electrode member (or discharging electrode) having a plurality of tooth-shaped electrode edges arranged in array along a longitudinal direction of and in facing relation to said photosensitive drum, a discharge regulating member (or discharge stabilizing shielding case) for regulating the region of corona discharging so that the corona discharge generated from said electrode edges is directed along the longitudinal direction of said photosensitive drum, and a mechanism for removably installing said edged electrode member in said discharge regulating member by slidably moving said edged electrode member relative to said discharge regulating member in a longitudinal direction thereof. With the arrangement being such that, the edge electrode member can be inserted into and removed from the charging device easily merely by slidably moving only the edged electrode member.
According to the present invention, the charging device may include a control grid for controlling the condition of charging the photosensitive drum by the corona discharge. With a conventional charging device of scorotron-type, the control grid must be removed in replacing the edged electrode member and the electrode member replacement has been a troublesome work. According to the invention, however, the replacement does not require the removal of the control grid, thus the effect of the invention is remarkable in this respect.
In the charging device of the invention, the mechanism for removably installing the edged electrode member includes a structure for supporting the edged electrode member, which is provided in the form of a plate, in such a way that the edged electrode plate is insertable and removable with respect to a guide groove formed in the discharge regulating member. Thus, the mechanism for removably installing the edged electrode member can be constructed simple.
Furthermore, the discharge regulating member of the charging device according to the present invention may be supported by a cleaning process unit for cleaning the photosensitive drum by removing residual toner. Alternatively, the discharge regulating member may be supported by the body of an electrophotographic apparatus which has incorporated therein the cleaning process unit.
In the charging device according to the invention, the edged electrode member has an engagement portion (or groove) which is engageable with an insulating attachment and removably inserted into the discharge regulating member by means of the attachment.
According to the invention, the edged electrode member is made of stainless steel and includes an electrode holder (or electrode plate holder) made of insulating material including PPE and polycarbonate, and the edged electrode member is made integral with the electrode holder as a replaceable part.
The edged electrode member includes a plurality of replaceable units of electrode each having a single or a plurality of the tooth-shaped electrode edges and an electrode support which detachably supports such replaceable units of electrodes. This electrode support is conductive with the above replaceable units of electrode so that all such units of electrode are applied with the same voltage.
Still furthermore, according to the present invention, there is provided a rotatable roller adjacent to an opening through which the edged electrode member is inserted for cleaning the edged electrode member when being rotated by sliding movement of the edged electrode member. The rotatable cleaning roller includes at least a pair of such rollers which are disposed so as to sandwich therebetween the edged electrode member. Additionally, the discharging device includes a scraper for scraping off fouling substances from the rotatable roller.